The present invention is particularly intended for use on commercial vehicles, although it may be used on any internal combustion engine connected to multiple fuel tanks. In particular, diesel engines typically operate by drawing fuel from a fuel tank, combusting a portion of the fuel and then returning the unused, or uncombusted, fuel to the fuel tank. Depending on engine loading conditions, a substantial volume of fuel drawn from the tank is unused by the engine and returned to the fuel tank. Accordingly, such draw and return assemblies play a vital role in the operation of diesel engines.
Heavy duty commercial vehicles, such as long haul tractor trailers, typically include dual fuel tanks, also called saddle tanks, wherein fuel is drawn simultaneously from both tanks for combustion within the engine. To prevent uneven fuel tank levels, which may lead to air being drawn into the engine, a means of balancing return fuel flow, such as draw and bottom return tube assemblies, typically are installed in each of the dual fuel tanks. One prior art draw and return tube assembly comprises draw and return tubes connected to a flange at one end and connected by a bracket at another end opposite the flange. The tubes extend outwardly from the flange parallel to one another. The flange is mounted on an upper inside surface of the fuel tank such that the opposite, bracketed ends of the tubes extend downwardly into the fuel held within the lower portion of the tank. Draw and return lines are connected to the flange, and thereby are connected to the draw and return tubes.
The tube openings opposite the flange extend away from one another and are each positioned an equal distance from the flange so that the draw and return tube fuel openings are also each positioned an equal distance below the top surface of fuel held within the tank. In this arrangement, when the two tanks and the corresponding draw and return tube assemblies are each positioned at a similar horizontal level on the commercial vehicle, the pressure head of fuel positioned above the draw and return tube openings of each assembly will result in equal amounts of fuel being withdraw from each of the tanks and equal amounts of fuel being returned to each of the tanks. In addition, swedging or crimping of the end of the return tube opening opposite the flange will facilitate complete filling of the return tube. Accordingly, the draw and return tube assemblies of the prior art act as passive flow regulators for ensuring equal levels of fuel drawn and returned to each of the two saddle fuel tanks.
The bracket used to connect the parallel draw and return tubes of the prior art generally comprises front and rear curved plates which are not welded to the tubes but which capture the tubes between the plates. The two plates are connected to one another between the tubes by a nut and bolt. A disadvantage of the bracket is that it may become loose during normal driving conditions due to vibration of the fuel tanks on the truck. Once the bracket becomes loose it may damage the inside of the fuel tank or may produce an annoying rattling sound during operation of the vehicle. The loose bracket can only be fixed by cutting a hole in the fuel tank to access the bracket because the fuel tanks are welded closed once the draw and return tube assembly is installed. Another disadvantage is that the bracket is time consuming to install and requires the manufacture of additional parts such as the metal bracket sections and the nut/bolt, a rivet, or other such fastener. Additionally, when the bracket is installed so as to connect the draw and return tubes opposite the flange, the rectangular structure that is formed is relatively weak and may bend or deform under external loading conditions. For example, when the assembly is inserted into the fuel tank during installation, the tubes may become twisted with respect to each other and/or the flange, such that the flange is deformed and cannot easily be welded to the fuel tank. Vibration of the fuel tanks during normal driving conditions may also result in twisting of the tubes with respect to each other and/or the flange. There is a need, therefore, for a draw and return tube assembly having a rigid structure which can withstand the external forces on the assembly associated with installation and normal driving conditions. Moreover, there is a need for a draw and return tube assembly wherein the tubes can be quickly and easily secured together without a bracket.